1. Field of the Invention
The present invention relates generally to the preparation of ketones and more particularly to a method and apparatus for preparing unsymmetrical ketones such as methyl cyclopropyl ketone (MCPK). The invention also relates to a method of using such ketone preparation method in the preparation of a herbicidal or other agricultural compounds.
2. Description of the Prior Art
In general, unsymmetrical ketones are useful as intermediates for the production of numerous specialty chemicals. More specifically, methyl cyclopropyl ketone (MCPK) has a variety of current and potential future uses including, among others, the production of specialty agricultural and pharmaceutical compounds.
Numerous literature references cite and disclose various well-known processes for the preparation of ketones. These processes include oxidation of secondary alcohols, Friedel-Crafts acylation, reaction of acid chlorides with organo cadmium compounds, acetoacetic ester synthesis and decarboxylation from acids, among others.
Text and literature references also detail problems associated with using these processes to produce ketones. These include problems such as the unavailability and/or cost of raw materials, the requirement of multi-stage processing, the low conversion of the raw materials and/or the low selectivity of the desired ketones, and the production of corrosive or hard to separate products.
Ketone production processes have also been described in the patent literature. For example, U.S. Pat. Nos. 4,528,400 and 4,570,021 disclose a process for the preparation of unsymmetrical ketones by a catalytic vapor phase reaction using reactants such as ketones with carboxylic acids. However, laboratory trials using acetone and cyclopropanecarboxylic acid resulted in the production of high quantities of gamma-butyrolactone, several pentenones and pentanones, but no MCPK.
U.S. Pat. Nos. 3,410,909 and 3,453,331 disclose processes for the preparation of symmetrical and unsymmetrical ketones from aldehydes containing up to 8 carbons in a non-cyclic saturated aliphatic chain.
German Patent Disclosure No. P36 37 788.0 (1986) discloses a specific condensation reactor process for the preparation of methyl cyclopropyl ketone (MCPK) from cyclopropanecarboxylic acid or its derivatives. However, although examples from this patent show raw material conversion of from 58 to 99 percent and selectivity to MCPK of 42 to 75 percent, the liquid hourly space velocity (LHSV) or weight hourly space velocity (WHSV) values of less than 1 (i.e., 0.25 to 0.99) minimize the industrial usefulness of this condensation reactor process.
European Patent Application No. 0 085 996 also discloses processes for the preparation of unsymmetric aliphatic ketones at atmospheric pressures (or slightly above) and at relatively low WHSV.
Still further, a reported disadvantage of all vapor phase tube reactor processes is the xe2x80x9ccokingxe2x80x9d or deactivation of the catalyst and consequential xe2x80x9cpluggingxe2x80x9d of the reactors. This results in the loss of production hours while the catalyst is being regenerated or replaced.
Accordingly, there is a need in the art for a method and apparatus for the production of ketones, and particularly unsymmetrical ketones such as methyl cyclopropyl ketone (MCPK) which utilizes readily available and inexpensive raw materials, which eliminates or minimizes reactor plugging, which provides for high conversion rates and high selectivity to MCPK and which dramatically improves the rate of production.
In contrast to the prior art, the present invention relates to a method and an apparatus for producing ketones, and in particular unsymmetrical ketones such as MCPK which overcome the limitations of the prior art. Specifically, the method and apparatus of the present invention utilizes readily available and inexpensive raw materials, minimizes reactor plugging, results in high conversion and selectivity rates and provides for increased production of the desired ketone. Generally, the raw materials used in the method and apparatus of the present invention include an acid or aldehyde or their derivatives and a carboxylic acid.
More specifically, the present invention involves the preparation of methyl cyclopropyl ketone (MCPK) utilizing a tube reactor provided with a suitable catalyst ranging from about 1 percent to 25 percent by weight. The preferred raw materials or feed materials include cyclopropylaldehyde or its derivatives (such as cyclopropanecarboxylic acid) and acetic acid which are readily available through processes known in the art. These raw materials are fed into a catalytic tube reactor where they are exposed to the catalyst and react to produce the desired ketone and various co-products. Preferably, the new raw materials are fed from the bottom to the top so that the reactant materials flow vertically upwardly through the reactor. To minimize undesired co-products as well as xe2x80x9ccokingxe2x80x9d of the catalyst and thus xe2x80x9cpluggingxe2x80x9d of the reactor, the optimum reaction temperature of the reactant feed stream is determined and the catalyst bed is preheated to such optimum temperature prior to the introduction of the reactant materials.
To further minimize downtime of the production process during the regeneration of catalyst or during reactor maintenance or repair, multiple or side-by-side reactors are provided with means for selectively directing the reactant materials to one or the other and removing product and co-products from such selected reactor. This permits the non-selected reactor or reactors to be repaired and/or maintained and the catalyst therein to be regenerated, if needed.
In the preferred embodiment and method of the present invention, the reactor is a vapor phase tube reactor in contrast to a condensation reactor or a batch stirred reactor. Further, the reactant materials in the method and apparatus of the present invention are preferably fed into the bottom of the reactor and caused to flow upwardly through the reactor over the catalyst. With this configuration, it is possible to dramatically increase the LHSV or WHSV. This results in dramatically increased production rates.
Accordingly, an object of the present invention is to provide an improved method and apparatus for the preparation of ketones and in particular unsymmetrical ketones such as methyl cyclopropyl ketone (MCPK).
Another object of the present invention is to provide a method and apparatus for preparing MCPK in a tube reactor with a minimized incidence of reactor plugging.
Another object of the present invention is to provide a method and apparatus for the preparation of MCPK utilizing inexpensive and readily available reactant or feed materials.
A further object of the present invention is to provide an improved method and apparatus for the preparation of MCPK at high conversion rates and high selectivity to MCPK, with minimal undesirable co-products.
A still further object of the present invention is to provide a method and apparatus for the preparation of MCPK at high production rates so as to result in an economically attractive process.
A still further object of the present invention is to provide a method of using the above-described ketone preparation method to prepare a herbicidal or other agricultural compound.
These and other objects of the present invention will become apparent with reference to the drawing, the description of the preferred embodiment and the appended claims.